It's been awhile since I have had any serious problem with my 425 with the
exception of a fuse that just decided it was time to die. I replaced it and
all has been well since. In the past, I did have a problem with the bias
control board which burned itself up, most likely due to a lightning strike
or some other event. I simply replaced the whole board with a new one from
TT ($61.88 according to my notes) and that fixed the problem.
Other problems that have arisen over the years included the plate
transformer shorting (took out the diode board, too), which was a fairly
common problem. Shortly after it was returned from the factory for that
work, a disc capacitor on the HV meter shunt board got too close to the
chassis and blew up. I replaced all the caps with better ones, stuffed the
board and bent the components so that there was maximum space to the
chassis. I replaced the rubber grommets in fan body and mount to quiet it
down a bit.
Other than pilot lights, that's all that's gone wrong since 1989. Still
running on the same finals with 2kW key-down output! It's reduced to
standby use since I got an ACOM 2000A in March, but it was pressed into
service a couple of months ago when the ACOM quit and had to go east.
Ron N6IE
www.N6IE.com
----- Original Message -----
From: "David J Windisch" <davidjw@cinci.rr.com>
To: <tentec@contesting.com>
Sent: Sunday, October 14, 2007 2:44 PM
Subject: [TenTec] Titan 425 problems
> Hi, all concerned:
>
> This amp was built in 1994 or 1995, according to TT's service dep't. It
> sat
> apparently unused for years: no wear spots, no dings, no scratches, no
> finger jam anywhere, no tracks on bandswitch contacts, no silvery pilot
> lamps, and so on.
>
> When I fired it up for testing, the QSK was inoperative. This first
> repair
> effort was my initial contact with TT manuals and sorta-schematics*. The
> schematics omit parts and leave out nomenclature on some of the parts they
> do show. It took an effort to trace the QSK circuit out, going from board
> to board, and another effort to figure out just how the QSK works, even
> with
> the sorta-explanation in the manual. The eventual solution was to unwind
> an end-turn on an opened RF choke, and splice it.
>
> Second attempt at testing produced a bodacious BANG, from the amp deck, I
> think, and the primary fuses were toast. Didn't figure out what caused
> that
> bang. Replaced the fuses, and powered up without further incident.
>
> For the first year or so, I operated the amp on c-w at the low-voltage
> setting with 1500W out, and then, after another bodacious BANG followed by
> RF power drop-off to about half, I went to the high-voltage setting to get
> back to 1500W out again. Didn't find anything amiss -- at that time,
> anyway.
>
> There happened later another bodacious BANG, which turned out to be the
> traces to the step-start resistor in the power supply simply vaporizing.
> I
> replaced them with #12 jumpers.
>
> Last week, the power supply produced a couple more bodacious BANGs.
>
> I pulled it apart, and found a popped filter cap, which I think is C6. I
> noticed that one of the two resistors in parallel with C6 is 150 ohms, not
> 150K like all the others. The step-start resistor was also burned open,
> and
> the soft-start fuse was blown.
>
> TT quoted $35 a pop for the filter caps. They're available at better
> prices
> elsewhere.
>
> I removed the cap and jumpered its connections. Fired it up again, got HV
> OK, but the meter pegs in the grid-current position and the red OVERDRIVE
> lamp illuminates. Same after removing the tubes.
>
> While looking into that, I noticed what may have produced the bodacious
> BANG
> followed by power dropping, mentioned earlier: there had been an arc and
> carbonization where the plate RF choke plate-side lead was run (too) near
> the middle of the choke body. Wire-brushed the choke body windings, and
> they looks OK under magnification.
>
> Any one out there have any ideas about the grid meter problem? I've
> searched the archives on "titan or 425" and seen nothing except that it
> happens.
>
> TIA & 73, Dave,
> N3HE
>
>
>
> *Afaik, I have the matching manual.
>
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>
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